I use 4 Asus Prime Z270-A with 8 GPUs (7 x PCIE + 1 M.2 -> PCIE adapter).
That's a very expensive mother board.
My a88x-g45 have 6 pcie but can only support 5. With extension it sort of support 6
The z270-A is all that I will use. I have had great luck with it so far. I have 6 mining computers going now with between 6-8 Nvidia GPUs. I am not going to sweat ~$20-50 for a better MoBo when I am spending 4-6k on the overall computer... I went with what I knew would work. Period.
I like your confidence. Not too expensive. Only 1.9 million. Not much more expensive than my A88x.
Anyone using AMD? Any AMD board that also works well?
I too used to use asrock btc. Never have problems with 6 GPU. I never tried using it for 7 to 8 GPU.
In terms of power consumption for high end cards, it is better to use 6 GPU.